Field of the Invention
The present invention relates to an organic light emitting display apparatus. More particularly, the present invention relates to a top emission type organic light emitting display apparatus and a method of manufacturing the same.
Discussion of the Related Art
Organic light emitting display apparatuses are self-emitting apparatuses, have low power consumption, a fast response time, high emission efficiency, high luminance, and a wide viewing angle.
The organic light emitting display apparatuses are classified into a top emission type and a bottom emission type, based on a transmission direction of light emitted from an organic light emitting device. In the bottom emission type, a circuit element is disposed between an emission layer and an image displaying surface, and for this reason, an aperture ratio is lowered. On the other hand, in the top emission type, the circuit element is not disposed between the emission layer and the image displaying surface, and thus, an aperture ratio is enhanced.
FIG. 1 is a schematic cross-sectional view of a related art top emission type organic light emitting display apparatus.
As illustrated in FIG. 1, a thin film transistor (TFT) layer T which includes an active layer 11, a gate insulation layer 12, a gate electrode 13, an interlayer dielectric 14, a source electrode 15, and a drain electrode 16 formed in an active area AA on a substrate 10, and a passivation layer 20 and a planarization layer 30 are sequentially formed on the TFT layer T.
An anode electrode 40 and an auxiliary electrode 50 are formed on the planarization layer 30. The auxiliary electrode 50 decreases a resistance of a cathode electrode 80 to be described below.
A bank 60 is formed on the anode electrode 40 and the auxiliary electrode 50 and defines a pixel area. An organic emission layer 70 is formed in the pixel area defined by the bank 60, and the cathode electrode 80 is formed on the organic emission layer 70.
In the top emission type, light emitted from the organic emission layer 70 passes through the cathode electrode 80. Therefore, the cathode electrode 80 is formed of a transparent conductive material, and a resistance of the cathode electrode 80 increases. In order to decrease the resistance of the cathode electrode 80, the cathode electrode 80 is connected to the auxiliary electrode 50.
The gate insulation layer 12 and the interlayer dielectric 14 are formed in a pad area PA on the substrate 10, a signal pad 90 is formed on the interlayer dielectric 14, and the passivation layer 20 is formed on the signal pad 90. A hole is provided in the passivation layer 20, and the signal pad 90 is exposed to the outside through the hole. Since the signal pad 90 should be connected to an external driving circuit, the signal pad 90 is exposed to the outside by forming the hole in the passivation layer 20.
The related art top emission type organic light emitting display apparatus has the following problems.
Since the signal pad 90 should be connected to the external driving circuit, a top of the signal pad 90 is exposed to the outside. For this reason, the top of the signal pad 90 is corroded, and the corrosion is spread to another area. A metal layer which is excellent in corrosion resistance may be further formed on the top of the signal pad 90 so as to prevent the top of the signal pad 90 from being corroded, but in this case, the number of processes increases. Also, an electrode layer which is the same as the anode electrode 40 may be formed on the signal pad 90 through the same process so as to prevent the top of the signal pad 90 from being corroded without an increase in number of processes, but even in this case, it is unable to prevent corrosion from being spread through a side surface of the electrode layer.
Moreover, in order to connect the signal pad 90 to the external driving circuit, the top of the signal pad 90 is exposed by forming the hole in the passivation layer 20. But when the hole of the passivation layer 20 is previously formed, an etchant for pattern-forming the anode electrode 40 flows through the hole and damages the signal pad 90. In order to prevent the damage, a process of forming the hole of the passivation layer 20 for exposing the top of the signal pad 90 may be separately performed after a process of pattern-forming the anode electrode 40 is completed, but in this case, a separate mask process is added.